OLED-based displays are currently being considered for use in many applications which presently employ liquid crystal displays (LCDs). OLED-based displays can provide brighter and clearer images than liquid crystal displays and also need less power. However, OLEDs are susceptible to damage resulting from exposure to oxygen and moisture. Such exposure may lead to a reduction in the useful life of the light emitting device. Therefore, hermetic sealing is one of basic requirements for long term performance of OLEDs.
Efforts have been made to hermetically seal OLED-based displays with organic materials, such as epoxy resins. An alternate technology with substantially better performance has been developed by Corning Incorporated, the assignee of this application. In accordance with this approach, a frit-containing paste is made by mixing glass particles, filler particles, e.g., crystalline particles, and a vehicle, e.g., a vehicle comprising one or more solvents and one or more binders and/or dispersing aids. The paste is dispensed on a first substrate (e.g., a first glass sheet) and is sintered using, for example, a high temperature furnace to produce a sintered frit pattern.
The resulting assembly, known as a frit cover glass or simply a cover, is combined with a second substrate (e.g., a second glass sheet) carrying one or more OLED devices. The cover and the second substrate are sealed together by exposing the sintered frit pattern to laser energy. In particular, a laser beam is scanned (traversed) over the sintered frit pattern to locally raise the temperature of the sintered frit above its softening point. In this way, the sintered frit adheres to the second substrate and forms a strong seal between the cover and the second substrate. Since the sintered frit is a glass and ceramic material, as opposed to an organic material, the penetration of oxygen and moisture through the frit seal is much slower than through the epoxy seals previously used to encapsulate OLED devices.
The sealing of larger size OLED devices, such as full-size TVs having a diagonal of, for example, 14 inches or larger, is more challenging than sealing smaller OLED devices, such as those used in cell phones, PDAs and other mobile electronic devices. For a typical small OLED device, a sintered frit with a sealing width of around 0.7-1.0 mm has proved sufficient. In particular, these sealing widths have been found to provide a sufficient moisture and oxygen barrier to allow a typical display to operate successfully for 1-3 years. In addition, such sealing widths provide sufficient mechanical strength for these smaller devices. The small sealing widths are also compatible with the limited space available on small OLED devices for sealing. For example, for a typical small OLED device, the edge area that can be dedicated to sealing has a width of only 1.0-1.5 millimeters.
In comparison to small devices, larger size OLED devices such as TVs require longer service times and have more demanding mechanical requirements. As a consequence, a need has arisen for large size packages for sensitive electronic components, such as OLEDs, which have seals that are stronger and/or provide greater protection from influx of water and oxygen. The present invention addresses this need.